Orthodontic aligner fabrication by overlay method

ABSTRACT

The orthodontic alignment of misaligned teeth includes preparing a digital and/or physical overlay model which is the superimposed positioning of the patient&#39;s original misaligned dentition with the target or final position. The superimposition of one upon the other creates an open space through which teeth may move in a natural manner, allowing for a treatment plan that takes into account the physical interaction of one tooth with another or the differences in tooth movement rates due in part to differences in underlying bone density or the like. An aligner tray fabricated using the model will likewise represent the before and after tooth positions and will also have the open space to allow tooth movement. Force exerting structures are preferably placed into the aligner tray to impinge upon the patient&#39;s teeth in a prescribed manner when the aligner tray is inserted into the patient&#39;s oral cavity.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Ser. No. 13/391,322 which isa national stage application of PCT/US2010/046175 filed Aug. 20, 2010and which claims the benefit of U.S. Provisional Application No.61/274,821 filed Aug. 21, 2009, entitled “ORTHODONTIC ALIGNER ANDMETHOD”; and U.S. Provisional Patent Application No. 61/307,668 filedFeb. 24, 2010 entitled “ORTHODONTIC ALIGNER FABRICATION BY OVERLAYMETHOD”, all of which are hereby incorporated by reference in theirentirety.

TECHNICAL FIELD

The present invention generally relates to the field of orthodontics.More particularly, the invention relates to an orthodontic alignmenttray and a method for fabricating such a tray and aligning teeth usingmanual or digital programming techniques.

BACKGROUND OF THE INVENTION

The field of orthodontics is well developed. Using conventionalbrackets, wires and the like, and based upon the nature of a patient'smisaligned teeth, a dental professional can determine a pathway forapplying appropriate forces to move teeth into better alignment. As theteeth are moved in such conventional procedures, they will often beblocked by other teeth. Because of the initial misalignment, it is oftennot simply a matter of moving, or repositioning, a tooth in onedirection to correct its position. Rather, the treatment plan most oftenmust account for physical contact between teeth as they move.

There have been developed methods of correcting the position ofmisaligned teeth using dental trays fabricated in a manner that a giventray will itself exert a force upon the misaligned teeth to causemovement. These include for example, the Invisalign® trays from AlignTechnology, Inc. of Santa Clara, Calif. Often these alignment trays arefabricated from a clear plastic material, and are provided in a seriessuch that each succeeding tray moves the teeth more or differently thanthe previous tray, in an incremental fashion so as to effect theprescribed treatment plan. Each tray therefore, will move certain teethfrom a starting or “before” position to a selected ending or “after”position. The “after” position is based solely upon the nature of theimmediately previous “before” position. Further, the shape and forceexerted by each successive aligner tray in the treatment process of theconventional system is based only upon the nature of where the previoustray left off in the moving of the teeth. There may be some target goalin mind as to where the dental professional wants to ultimately move theteeth, but until the very end of the patient's treatment procedure, thisfinal position and the initial starting position do not affect theincremental or intermediate treatment steps. That is, the conventionalsystem can be said to be “closed.”

Because of this, it has often been necessary therefore, to applyexcessive stripping to teeth in order to allow them to move in theapproximate direction desired. The results of excessive stripping areoften not aesthetically appealing or even healthy for the strippedteeth. While the conventional procedures will move teeth, they do notpermit the teeth to move in their more natural or open pathways.

It would be advantageous therefore, for an alignment tray to befabricated and used in a manner that allows for the open or naturalmovement of teeth. That is, the tray and the resulting procedure shouldmore readily and appropriately accommodate the variables to toothmovement including not only the initial misaligned position of a giventooth and the final desired position, but also the physical interactionthat exists between teeth or that will occur as the teeth move, thevariable nature of the underlying bone structure and the like.Heretofore, conventional orthodontic aligner trays have not allowed forthis type of natural tooth movement in orthodontic procedures.

Another practice used by orthodontists involves altering a polymericshell-type aligner beyond its original as-formed configuration.Typically the interior, tooth-contacting surfaces of tooth-accommodatingcompartments are formed in an aligner. The inside surface of any onecompartment completely surrounds and is in intimate contact with itstooth when the appliance is seated in position. For forces such as thosecreated through the installation of a single bump in an interior wall ofan aligner to be effective in moving the tooth, the interior wall on theopposite side of the compartment must be relieved or removed to allowthe tooth to move in that direction. The tooth will not move unlessobstacles have been cleared and free space is provided for that tooth tomove into. To handle such situations, orthodontists may alter alignersby cutting away material or blocking out portions of a tooth model, tocreate free space for a tooth to move into. Free space or windows arecreated by trimming away aligner material in the direction of desiredtooth movement. A window in an aligner will be created for example onthe labial side of a tooth if the treatment plan requires that a bump beformed on the lingual side. It would be advantageous as well to providean aligner tray with tooth compartments that include space into whichthe targeted teeth may move, without having to manually cut away traymaterial or block out portions of a tooth model when forming the tray.

DISCLOSURE OF THE INVENTION

It is therefore, an object of the present invention to provide analigner tray fabricated and used in such a manner as to accommodate thenatural or open movement of teeth. This and other objects of theinvention as will become apparent from the description to follow, arecarried out by the invention as hereinafter described and claimed.

According to the invention, an alignment tray is fabricated based upon amodel that is a physical overlay of both the initial misalignment (or anintermediate one) and a target or final position of the teeth where theyare ultimately desired to be moved. The model can be a physical model, adigital model or both. A tray fabricated from such an overlay model willhave a force bump or appliance of some kind that is placed into the trayto exert a selected force upon selected teeth to cause them to move asdesired. The tray therefore, is itself an overlay that includes both thestarting point of the teeth and the end point, but it is the forceexerting bumps or appliances fabricated into the inventive trays thatexert the tooth moving force. Because of this arrangement, the tray isan open system and allows for the more natural movement of teeth thatare resisted by the nature of the underlying bone structure and byinteraction with other teeth. Physical contact between teeth, differentmovement rates based upon such bone density and the like, are not onlypermitted but will be proactively planned for and even employed by thedental professional's prescription to effect the overall treatmentprocedure.

In one embodiment, a method of fabricating orthodontic aligner traysincludes acquiring an original digital model of a patient's teeth;segmenting the teeth represented by the digital model; repositioning atleast one of the teeth into correct alignment to create a final teethmodel, the final teeth model representing a final teeth position;superimposing the final teeth model with the original digital model tocreate a digital overlay model, the overlay model comprising a startingpoint defined by the original digital model and an end point defined bythe final teeth model; fabricating at least one aligner tray based onthe overlay model to define a tooth-receiving compartment within eachaligner; and inserting at least one force appliance into the at leastone aligner tray, the at least one force appliance positioned within thetooth-receiving compartment to exert a selected force upon selectedteeth.

In another embodiment there is an aligner tray for repositioning teethaccording to an orthodontic treatment plan. The aligner tray includes atray portion defining a tooth-receiving compartment within the trayportion and formed from a thermoformable plastic sheet. Thetooth-receiving compartment is based on an overlay model. The overlaymodel includes an original teeth position, a final teeth position andpath ways for each tooth. The original teeth position, the final teethposition and path ways for each tooth fall within the tooth-receivingcompartment of the aligner tray. The final teeth model represents atleast one segmented teeth being repositioned into correct alignment tocreate a final teeth model. The final teeth model is superimposed withthe original digital model. Force appliances are positioned within thetooth-receiving compartment to exert a selected force upon selectedteeth.

In yet another embodiment, a method of fabricating orthodontic alignertrays includes pouring a stone model of a patient teeth and scanning thestone model into a digital file using a scanning software system;segmenting the teeth represented by the digital model; measuring thetooth and arch width digitally; analyzing a case using inter-proximalreduction prescription (IPR) and desired tooth movements, reviewing IPRprescription for validity; performing IPR if prescription is acceptable;and developing and communicating a treatment plan; repositioning atleast one of the teeth into correct alignment to create a final teethmodel, the final teeth model representing a final teeth position;superimposing the final teeth model with the original digital model tocreate a digital overlay model, the overlay model comprising a startingpoint defined by the original digital model and an end point defined bythe final teeth model; creating a rapid prototype model for a pluralityof identical aligner trays based on the overlay model to define atooth-receiving compartment within each aligner; vacuum thermoformingeach of the aligner trays over the physical overlay model using a vacuumforming machine and a plastic thermoforming sheet; programming at leastone force appliance in at least one aligner tray to incrementallyreposition the selected teeth incrementally according to the treatmentplan; and inserting the at least one force appliance into the at leastone aligner of the plurality of aligner trays, the at least one forceappliance positioned within the tooth-receiving compartment to exert aselected force upon selected teeth.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a flow chart of one embodiment of the overlay method offabricating aligner trays.

FIG. 2 is a top plan view of a model of a patient's dentition beforeorthodontic treatment according to the present invention.

FIG. 3 is a top plan view of a model of a patient's dentitionrepresentative of the final tooth position which is the final or targetposition according to the prescribed orthodontic plan for the patientwhose dentition is represented by the model of FIG. 2.

FIG. 4 is a top plan view of a digital representation of both the modelof FIG. 2 and the model of FIG. 3 superimposed one upon the other,thereby creating space between the position of the teeth as in the modelof FIG. 2 and the position of the teeth as in model of FIG. 3.

FIGS. 5a, 5b, 5c show multiple views of a physical overlay model of thedigital superimposed model of FIG. 4.

FIG. 6 is a top plan view of an aligner tray prepared from the physicaloverlay model of FIG. 5.

FIGS. 7a, 7b and 7c are close up views of one portion of the aligner ofFIG. 6, with force bumps inserted therein.

FIGS. 8a, 8b and 8c show an exemplary series of tacks.

FIG. 9 is a flow chart of another embodiment of the overlay method offabricating aligner trays using digital imaging.

FIG. 10 shows a CAD image of the patient's teeth.

FIG. 11 shows the CAD image of the patient's teeth from FIG. 10including a force bump.

FIG. 12 shows the CAD image of the patient's teeth from FIG. 10including reference lines, centerlines, and two-dimensional andthree-dimensional splines.

FIG. 13 shows a section of the CAD image of the patient's teeth fromFIG. 10 including a divot marker.

FIG. 14 shows an exemplary retaining tack, also referred to as alignerauxiliary.

FIG. 15 shows a tack and the virtual model as one solid structure.

FIGS. 16a, 16b and 16c show an exemplary series of an alternate form oftacks.

PREFERRED EMBODIMENT FOR CARRYING OUT THE INVENTION

A method according to the present invention includes several steps. Notall of the following steps are necessary and there are alternatives. Forexample, although the invention will be characterized as employing, forexample, a digital dental model and software to create the inventivemodels and aligners, it will be appreciated that the procedures can beaccomplished manually. Similarly, fabrication methods of physicallycreating the various inventive components can be by conventional rapidprototyping procedures or the like as will be discussed, again with theunderstanding that other fabrication techniques can be employed withinthe scope of the invention.

The inventive method employing the inventive components therefore,preferably includes receiving, obtaining or otherwise preparing a stoneor plaster model of the patient's dentition or even a conventionaldental impression thereof. While it is possible that the invention canbe carried out by a dental professional, the invention will be describedherein as being carried out in conjunction between a dental professionaland an extension of the professional such as a laboratory. It is to beunderstood that no distinction should be made or implied as to such adivision and the nature of the present invention is the whole, not theindividual participants. Both a division between a dental professionaland a laboratory and the carrying out of the invention by a singleperson or entity, or indeed between any multiple entities is within thescope of the invention without limitation.

When received, each case is inspected to ensure that all the propermaterials are included with the shipment, including as may be employed,physical models, impressions, digital scans of the dentition or thelike. Again, this may vary depending upon the above described divisionof labor and is not itself a necessary limitation of the invention. Forexample, cases that are received by a laboratory as impressions onlywill have stone models poured and then each model will be individuallyinspected to determine that the model is complete and an accuraterepresentation of the patients dentition. Alternatively, if the modelitself is received from an upstream source, then it will be soinspected. Digital scans of the dentition will be treated in the samemanner.

Referring to FIG. 1, the overlay method, generally indicated as 100, forfabricating aligner trays for orthodontic treatment is described asfollows. As described above, patient's dental impression is received andinspected. At step 102, a stone model 10 (FIG. 2) is poured from theimpression. At step 104, stone model 10 is then scanned into a digitalfile, e.g., using a scanning software system such as 3Shape R700, by3shape A/S, of Copenhagen, Denmark (hereinafter referred to as 3shape),a 3D scanner system developed to scan dental stone models. At step 106,the tooth and arch width are measured digitally, e.g., using OrthoAnalyzer software. At step 108, the patient's malocclusion is analyzedusing prescribed inter-proximal reduction prescription (IPR) and desiredtooth movements. At step 110, representations of the teeth are manuallysectioned or segmented using software, e.g., Ortho Analyzer NextGeneration software from 3 shape.

The type of scanner or scanning is not necessarily a limitation of thepresent invention. One useful and commercially marketed scanner is, forexample, the OrthoPlex orthodontic digital modeling solution availablefrom DENTSPLY International of York, Pa. The OrthoPlex scanner and itsassociated software, creates a three-dimensional (3D) digital model thatcan be accessed by a computer or the like, and is stored as an STL file.An STL file is a conventional format often used by stereolithographysoftware to generate information needed to produce 3D models onstereolithography machines. While it is not necessary to use this fileformat, the format is useful in conjunction with the present inventionbecause of the preferred use of a stereolithography step as will bedescribed below.

At step 112, the IPR prescription is reviewed for validity. Next, atstep 114, if the prescription is acceptable the IPR is done manually,and necessary changes are approved by the dentist. At step 116, atreatment plan is developed and communicated to the dentist, using a setof clinical verification forms. Next, at step 118, the manuallysegmented representations of the teeth are physically moved into correctalignment to create a final model 12 (FIG. 3). Final model 12 may thenbe scanned to create a final tooth position digital model correspondingto final model 12. At step 120, the final tooth position digital modelis superimposed with the digital model of the original model 10 tocreate a digital overlay model 14 (FIG. 4). In an exemplary embodimentdigital overlay model 14 may be created using Materialise 3-matic, acustom software solution. The digital overlay model 14 may be suitablefor rapid prototyping, e.g., using Materialise 3-matic. Next, at step122, a rapid prototype or physical overlay model 16 (FIG. 5) is createdof the overlay configuration.

Physical overlay model 16 is then created by a rapid prototyping method.The rapid prototyping technique should be understood to be alltechniques whereby an object is built layer by layer or point per pointby adding or hardening material (also called free-form manufacturing).The best known techniques of this type are: stereolithography andrelated techniques, whereby for example a basin with liquid syntheticmaterial is selectively cured layer by layer by means of acomputer-controlled electromagnetic beam; selective laser sintering,whereby powder particles are sintered by means of an electromagneticbeam or are welded together according to a specific pattern; or fuseddeposition modeling, whereby a synthetic material is fused and isstacked according to a line pattern.

Next, at step 124, a plurality of identical aligner trays 18 (FIG. 6)are fabricated using the physical overlay model 16. The number ofaligners varies from case to case. In one exemplary embodiment, alignertray 18 is preferably thermo-formed over the physical overlay model 16using, for example, an Essix vacuum forming machine and Essix Aceplastic thermoforming sheets. Both the sheets and the thermoformingmachine are commercially available from DENTSPLY International, and thethermoforming process itself is conventional and known in the dentalart. Using the physical overlay model 16 to produce aligner tray 18results in a clear pathway of space from the teeth positions beforepatient treatment to the teeth positions after treatment, created toallow for tooth movement, as was already discussed.

At this point in the fabrication process, aligner tray 18 is passive,i.e., aligner tray 18 will not exert forces on the teeth when insertedinto the patient's mouth. The original and the final tooth positions aswell as the path ways for each tooth fall within the boundaries of thealigner. The aligner trays 18 are then thermoformed using the overlaymodel 16. Each aligner tray 18 is identified as step 1, 2, 3, etc. Theresulting aligner tray 18 does not actively engage any single tooth forinducing tooth movement, but generates a passive aligner tray 18 withwhich preselected individual teeth can be moved. Movement of thepreselected individual teeth is induced by programming or formingfeatures in the passive aligner, such as bumps 20 (see, e.g., FIG. 7a ),to apply pressure to teeth. Features may be formed, for example, byusing the patented Hilliard thermoforming pliers system, which isdisclosed in U.S. Pat. No. 6,293,790 issued Sep. 25, 2001 to Hilliard,and U.S. Pat. No. 7,077,646 issued Jul. 18, 2006 to Hilliard, both ofwhich patents are incorporated herein by reference.

At step 126, after thermoforming aligner trays 18, force bumps 20 areprogrammed into each identified treatment aligner tray 18, e.g., asprescribed in a clinical verification plan from the treatment plan step.Programming force bumps 20 into aligner trays 18 may be done by manuallythermoforming each bump 20 in the lab using a thermoforming tool, forexample, a Hilliard Thermopliers®, available from DENTSPLYRaintree-Essix, of Sarasota, Fla. Aligner trays 18 that are thermoformedfrom overlay models 16 may be manually adjusted with the force bumps 20using the Thermopliers®. Aligner trays 18, inclusive of the manual forcebumps 20 are then sent to the dental professional. After the finalaligner configuration is inspected, a final retainer is thermoformedusing final model 12, and then aligner trays 18 and final retainer areshipped to the dentist.

It will be appreciated that the physical overlay model 16 may be createdin a completely manual process by otherwise conventional techniques. Inwhatever manner the physical overlay model 16 is prepared, the result isthat it is a representation of both the patient's starting teethposition and the target, final or end position, one superimposed uponthe other. It will be appreciated that there is an open area or spacebetween those structures representing the original tooth position andthose structures representing the final tooth position. This open natureof the physical overlay model 16 allows for the above described naturalmovement of teeth and the taking into account the physical contactbetween teeth, differences in underlying bone density and the like, aswill be appreciated from the following discussion concerning thepreparation of an aligner tray 18 using physical overlay model 16. Ofcourse, if desired, it would also be possible to control a fabricationmachine using digital overlay model 14 directly to create an alignertray 18, and still be within the scope of the invention.

After aligner tray 18 has been formed over physical model 16, alignertray 18 may be removed and trimmed in a manner conventional with dentaltrays. Once the aligner tray 18 is trimmed, force exerting structures ofsome kind are placed into the aligner tray 18 in a manner to carry outthe prescribed orthodontic tooth moving or repositioning procedure asthe patient inserts the aligner tray 18 into the oral cavity and wearsit therein for the prescribed length of time. For example, distortionsin the tray material itself may be created to provide force bumps 20,preferably by the use of Hilliard thermo-forming pliers, also availablefrom DENTSPLY International. The bumps are placed at predeterminedlocations to create the desired movement of each tooth according to theprescribed treatment plan. Each force bump 20 will push a tooth into thepathway of space in the aligner created by the use of the physicaloverlay model 16. It will be appreciated that force exerting structuresmay include additional plastic attachments, pins, buttons or indeed anystructure useful and capable of applying an appropriate and selectableforce in an orthodontically acceptable manner. The aligner tray 18 or anew aligner tray (not shown) can be provided to the patient having theforce exerting structures adjusted according to the patient's treatmentplan.

In another embodiment of the invention, an aligner tray 18 is preparedas above, but is provided with force exerting structure in the form of aflowable material that can be used to fill or partially fill the alignertray 18. The flowable material can be shaped or even selectivelyhardened to provide the desired force to be exerted upon the selectedtooth or teeth to carry out the prescribed treatment plan. It is evenpossible that flowable materials of different durometer ratings orviscosities can be provided to achieve parts or different parts of theoverall patient treatment plan. In a similar fashion, in the instancewhere there is a void or space between teeth, or perhaps where extraspace is needed, the physical overlay model 16 may be covered orpartially covered in such a material, or even a standard dentalimpression material, such that additional or different selected spacemay be introduced into the subsequently fabricated aligner tray 18.

U.S. Pat. No. 6,293,790 entitled “Heated Orthodontic Pliers”, andincorporated by reference, discloses a series of steel dental pliersuseful for modifying polymeric shell aligners. Thermopliers® refers to agroup of hand-held steel instruments that in use are heated to apredetermined temperature. Once heated, they are directed to an alignerto effect local heat-softening and thermal flowing of the alignerstructure thereby forming various types of useful features andalterations.

Rotations, in contrast to torqueing and tipping-type corrective forces,are more difficult to deliver using aligners. To augment an aligner'scapability to fully correct a rotation, orthodontists use one of the setof Thermopliers® configured to thermoform a small, sharp, inward-facingbump 20 in the structure of the aligner (see FIG. 7a ). Such athermoformed bump 20 requires skillful manipulation of the pliers toform a bump 20 positioned in the wall of a tooth-receiving compartmentof an aligner. When such a modified aligner is seated in position in themouth, the location of the bump 20 is such that it produces a forcevector to mechanically rotate the tooth.

To illustrate the use of such bumps in treatment, a disto-linguallyrotated maxillary lateral left tooth may be rotated by placing a firstbump 20 at the disto-incisal position to contact the tooth on itsdisto-lingual surface, and a second bump 20 formed at the mesio-labial,incisal location of the same compartment. During treatment, such a pairof co-working bumps cooperate to create a coupled rotational force in amesial-lingual direction according to this example. The correctionneeded to fully correct a rotated tooth can be achieved by activatingthe aligner through using the appropriate Thermoplier as described.Progressive activation in this manner serves to counter force levelreduction resulting from the dissipation of corrective forces as theteeth respond and move. Such revisions also serve to maintain moreconstant biological forces on the teeth being repositioned, which isgenerally thought to promote the most rapid tooth movement. A set ofaligner trays 18 may be typically produced with programmed bumps in eachaligner tray 18 for a course of treatment, as described above. However,in alternate embodiments a single aligner tray 18 may be modified, e.g.,by adding features or enlarging existing features. One or moremodifications will allow a single aligner tray 18 to serve for multipleprogressive treatment phases before being spent and discarded.

Bumps as described serve to focus energy stored locally in the region ofthe aligner's structure adjacent to a bump 20. The inward-projectingbump 20 causes an outward flexing of the aligner material in a regionaway from the tooth surface. Configured in this way, bumps gather storedenergy from a wider area and impinge that energy onto the tooth at themost mechanically advantageous point, thus focusing corrective forcesmost efficiently.

In another example, in which the tooth is essentially in its properposition and only requires torqueing to a desired orientation, a bump 20may be installed near the incisal edge on the lingual side, the incisaledges of the crown will slowly respond by swinging into the relief ofthe window on the labial.

Commonly owned U.S. Pat. No. 6,702,575, entitled “Orthodontic AlignerAuxiliary System”, teaches other techniques for extending the usefulnessof aligners and is hereby incorporated by reference. The '575 patentinvolves the installation of separate auxiliary devices into thephysical structure of conventional aligners and related methods forpreparing aligners to accept and retain such devices. To follow is adescription of how these devices may be incorporated into the overlaymethod and aligner trays 18 formed using the overlay method, along withdescriptions of how they function and the preparatory steps that mustfirst be taken so that such devices can be installed into an aligner'sstructure.

The '575 patent involves the introduction of a group of small devicesthat are intended to be strategically positioned and attached to analigner's structure. Such devices are termed “aligner auxiliaries.”Prior to installing such devices, a doctor may assess the progress of acase at mid-treatment, for example and in particular, make note ofproblem areas where the desired tooth response is lagging or instanceswhere particular teeth are stubbornly not moving in response totreatment forces. Aligner auxiliaries are installed in those locationsto amplify and focus corrective forces of the aligner to enhancecorrection. For example, an auxiliary known as a tack 30 (FIGS. 8a, 8b,and 8c ) can be installed after a hole of a predetermined diameter ispierced through a wall of a tooth-containing compartment of an aligner.The diameter of the hole is slightly less than the diameter of a shankportion of the tack. Next, a tack-installing plier is used to forciblypop the retentive head of the tack 30 through the hole, resulting in thetight and secure retention of the tack within the aligner structure. Thetack pops into position where it is tightly retained in the alignerwithin the punched hole. Such progressively-sized tacks and otherauxiliary devices are commercially available to orthodontists who usethem to augment and extend the tooth position correcting forces ofaligners.

The installation of an auxiliary device such as a tack 30 to achieve thedelivery of tooth-moving forces is similar to the effect achieved byinstalling the bump 20 described earlier. The use of a separate tack,however, permits the forces delivered to a tooth to be progressivelyregulated over time by using a sequential series of progressively longertacks 30 as shown in FIGS. 8a, 8b, and 8c and described in the '575patent. A series of aligner trays 18 may be generated, as is describedabove with respect to bumps. As the energy stored in the aligner'sstructure adjacent to the tack is spent through movement of the tooth,the aligner with the longest of three tacks can be installed after themedium tack is spent, removed and discarded.

Digital Overlay Method

Referring next to FIG. 9, in another aspect of the invention an overlaymethod of fabrication of aligners for orthodontic treatment may beimplemented digitally, using the following method 200. Initially, apatient's dental impression is received and inspected. At step 202, astone model 10 is poured from the impression. At step 204, the stonemodel is scanned into a digital format representing the originalposition of the teeth in the patient's maloccluded dentition, e.g.,using a scanning software system such as 3Shape R700, by 3shape, a 3Dscanner system developed to scan dental stone models. At step 206, thetooth and arch width are measured digitally, e.g., using Ortho Analyzersoftware. Next, at step 208, the patient's malocclusion is analyzedusing prescribed inter-proximal reduction prescription (IPR) and desiredtooth movements. At step 210, representations of the teeth are digitallysectioned using software, e.g., Ortho Analyzer Next Generation softwarefrom 3shape. In an alternate embodiment, the digital file may be createddirectly from an intra-oral scan of the patient's dentition, providingthe original maloccluded dentition in a digital format without having tocreate and scan a stone model 10.

The method proceeds from step 210 to step 212, in which the IPRprescription is reviewed for validity. At step 214, IPR is donedigitally if the prescription is acceptable, and necessary changes areapproved by the dentist. At step 216, a treatment plan is developed andcommunicated to the dentist, using a set of clinical verification forms.At step 218, segmented representations of the teeth are digitally movedinto correct alignment to create a final model 12. Final model 12 maythen be scanned to create a final tooth position digital model. At step220, the final tooth position digital model is superimposed with theoriginal model to create a digital overlay model 14. The digital overlaymodel 14 may be suitable for rapid prototyping, e.g., using Materialise3-matic. At step 222, a rapid prototype or physical overlay model 16 iscreated of the overlay configuration. The physical overlay model 16 isthen created by a rapid prototyping method.

Next, at step 224, a plurality of identical aligner trays 18 arefabricated, e.g., using the physical overlay model 16. The physicaloverlay model 16 is used to create an aligner tray 18. The number ofaligners varies from case to case. In one exemplary embodiment alignertray 18 is preferably thermo-formed over the physical model 16 using forexample, using an Essix vacuum forming machine and Essix Ace plasticthermoforming sheets. As described above with respect to the manualoverlay method, using the physical overlay model 16 to produce alignertray 18, results in a clear pathway of space from the teeth positionsbefore patient treatment to the teeth positions after treatment, createdto allow for tooth movement, as was already discussed.

At this point in the fabrication process, aligner tray 18 is passive,i.e., aligner tray 18 will not exert forces on the teeth when insertedinto the patient's mouth. The original and the final tooth positions aswell as the pathways for each tooth fall within the boundaries of thealigner. The aligner trays 18 are then thermoformed using the overlaymodel 16. Each aligner tray 18 is identified as step 1, 2, 3, etc. Theresulting aligner tray 18 does not actively engage any single tooth forinducing tooth movement, but generates a passive aligner tray 18 withwhich preselected individual teeth can be moved. Movement of thepreselected individual teeth is induced by programming or formingfeatures in the passive aligner, such as bumps 20, to apply pressure toteeth (see FIGS. 7a-7c ). Features may be formed using the patentedHilliard thermoforming pliers system.

After thermoforming aligner trays 18, at step 226, force bumps 20 areprogrammed into each identified treatment aligner tray 18, as describedabove with respect to the manual overlay method.

Programming force bumps 20 into aligner trays 18 may be done by manuallythermoforming each bump 20 in the lab using a thermoforming tool, forexample, a Hilliard Thermopliers®, by DENTSPLY Raintree-Essix, ofSarasota, Fla. Aligner trays 18 that are thermoformed from overlaymodels 16 may be manually adjusted with the force bumps 20 using theThermopliers®. Aligner trays 18, inclusive of the manual force bumps 20are then sent to the dental professional. After the final alignerconfiguration is inspected, a final retainer is thermoformed using finalmodel 12, and then aligner trays 18 and final retainer are shipped tothe dentist.

In one embodiment the stone models of the patient's dentitions may bescanned and stored in a digital computer-aided-design (CAD) file format.The patient's models are then subjected to a scanning process and theresulting data for the upper and lower arches is stored in digitalformat to create a CAD model of at least a portion of the patient'sdental anatomy. The most frequently used means of converting an actualphysical object into digital code for three-dimensional imaging, namelylaser scanning, as well as other methods, first produce what is known asa “point cloud”. The software will strive to rationalize the location ofpoints known to be associated with features of the actual object withthat same point located in other scans obtained while scanning theobject from multiple angles. All of the points taken from multiple scansfrom different vantage angles will be overlapped and interpreted,allowing the software to create a complex surface represented by a cloudof perhaps a half-million individual points. Each of the points isassigned specific coordinates in three-dimensional space relative to apredetermined point of origin on the physical stone model of thepatient's teeth. It should be understood that all of the pointstheoretically fall on the surface of the part being imaged and byviewing all of the points, a rough sort of visual image of the originalpart can be seen visually on a computer monitor.

Other software available to a CAD technician can be used to furtherprocess the point cloud into what is known as a true solid model thatcan be later manipulated and modified using solid-modeling CAD software.FIG. 10 is an example of the resulting CAD image 15 of the patient'steeth. However, some of the operations that a CAD technician needs toaccomplish in processing an orthodontic patient's case can be performedat the initial point cloud phase.

As an example of how a point cloud can be manipulated according to thepresent invention, commercially-available software permits a CADtechnician to identify a region of points. The points inside such aregion are assigned different properties than unaffected points outsidethe region. For example, a CAD technician may identify a region ofpoints representing the occlusal region of a particular tooth from ascanned-in set of models. That region of points may be approximately thesame size as an inwardly extending bump 20 or outwardly extendingbubble, for example. Conventional algorithms affecting how points withinthe identified region are dynamically linked allow the technician tograb any one point located near the center of the region and that pointis then considered a master point. For example, the technician wouldaccomplish this through manipulation of a digitizing puck on adigitizing tablet or with a mouse. The technician would tug on thatmaster point. When tugged, all of the surrounding linked points withinthe identified region will to one degree or another move along with themaster point being tugged in proportion to their relative distance fromthe master point. For example, points relatively near the master pointwill move the most whereas points more remote from the master point willmove only a little. From this action, all of the points within theidentified region will move to one degree or another and thereafter, thepoints inside the region will have moved inward into the general shapeand appearance of a force bump 20 as shown in FIG. 11.

Similarly, an outward-extending bubble can be formed by the technicianby pulling a master point rather than pushing. Again, all of the pointsin a region will tag along to one degree or another as determined by thelogic of how the points within the region are dynamically linked.

As an alternative a hand-held scanning wand (e.g., the Orometrix®system)can be used in the orthodontist's office to directly scan the patient'soral anatomy. The resulting digital data is then electronicallytransmitted to the orthodontic service center. Similarly, it is possiblefor the scanning methods described above to be directed to scanning theconcave negative troughs directly from a set of dental impressions.

Due to the many degrees of activation afforded by the array of varioustypes of direct aligner alterations that can be made, such as withThermopliers®, and the array of separate auxiliary devices, progressivetooth movement may be achieved through the use of an overlay alignertray 18 having the hybrid original and final geometries combined.Multiple aligner trays 18 of the singular overlay aligner tray 18 canthen be sequentially programmed to include bumps, or tacks, inserts andthe like, as described above. For example, direct tooth contactingshort, medium and long tacks 30 (FIGS. 8a, 8b and 8c ) may be used, orother devices with sequential elasticity (FIGS. 16a, 16b, and 16c ) maybe used. Various threaded devices may be progressively activated, as cana jackscrew. Stainless steel or metallic auxiliaries such as acantilever arm can be progressively activated over time as is typical oforthodontic hardware. In this manner, aligner trays 18 producedaccording to the present inventive methods can be considered as“progressive” in orthodontic treatment.

As a technician analyzes a patient's models visible on the computermonitor, the technician would see images representing a malocclusion atthe beginning of treatment or partially-treated occlusion. Since themodels can be used to generate a true three-dimensional image of thepatient's oral anatomy, as shown in FIG. 10, the technician candynamically rotate the dental topology for close scrutiny. Thetechnician can sight across the virtual teeth from literally any angleor vantage point, including vantage points that would be anatomicallyimpossible with a living patient, such as viewing from the rear of themouth or vantage points occluded by bone and tissue.

Since the model exists in a virtual three-dimensional CAD space, thetechnician can assess the case and take measurements to quantify variouscriteria for treatment, such as upper versus lower arch length, archwidth, inter-canine width, arch morphology as well as degree ofopen/deep bight, molar relationship, over jet, curve of Spee, andsymmetry. The technician can also note primary, deciduous, missing andimpacted teeth, and consult statistical anatomical values, all in lightof the attending doctor's instructions/prescription. For example, theCAD software can be used by the technician to sketch any number ofreference lines, centerlines, and such, as shown in FIG. 12. Thedentition can be interrogated just like any solid model can bedimensioned with CAD software. As depicted in FIG. 12, two-dimensionaland three-dimensional splines may be strung between features of thescanned-in surfaces. The technician may zoom in and magnify particularfeatures for examination and decision making. Any number of features maybe dimensioned from technician-specified reference lines or relative toother features of the anatomy. Generally, based on this process ofmeasuring and examination, a technician may thereafter refer to and useknown statistical data of established anatomical dental norms or othernorms such as typical torque, tip prominence and arch form values foundin patients of the same age, sex and ethnic characteristics. All ofthese activities are undertaken to arrive at optimal decision-making inpreparation to designing a number of aligners and aligner auxiliaries toachieve treatment objectives.

A CAD technician can make decisions such as where best to form variousbumps, bubbles, windows, various holes for activation devices, standoffsand outset lands and so on, that together will serve to activate toothmovement, as well as locate the myriad of aligner auxiliaries 30described above, with the aid of all of the technology and digital toolsavailable at his or her disposal. The technician has analytical,measurement, and investigative tools at hand. Thus the technician candetermine where to locate aligner features such as inwardly extendingbumps. Various types of aligner auxiliaries 30 can also be optimallylocated by the CAD technician.

For example, the technician may identify a labially-flaired anteriortooth that requires uprighting. To accomplish such a correction with asuck-down aligner, the technician may opt to have a tack located at anexact position relative to that tooth. The technician will determine theideal location that will maximize the tack's mechanical advantage foruprighting, and a location indicator (e.g., a divot marker 32) will becreated exactly at that point. For that matter, the optimal location forpiercing the aligner for the full array of aligner auxiliaries can bestbe determined by the CAD technician rather than the doctor attemptingsuch an analysis manually while simultaneously addressing all of theother concerns and distractions involved when working with a realpatient.

In general, the technician manipulates the CAD model to create aprogressive series of aligners with features for accommodating alignerauxiliaries for sequential use during the patient's orthodontictreatment. The technician working with the CAD system can createmultiple virtual models representing the incremental, but progressivemovement of teeth between the “as scanned” occlusion and the desiredfinal occlusion. In addition, the technician can use the CAD system tomove specific teeth according to treatment objectives to desiredpositions as would be considered ideal at the end of a specific phase oftreatment for which aligner auxiliaries are to be employed. Movementsaccomplished by the CAD technician can include correction of individualteeth in terms of torque, tip, prominence, rotation, bodily movement,and to a degree, intrusion and extrusion.

For example, the technician has the capability of zooming in on finedetail so that the computer monitor and the technician's field of visionaccommodate only a single tooth being analyzed. In order to establishthe optimal location for aligner auxiliaries, such as the pop-in tacks,a divot marker 32 can be installed on the model by the technician, asdepicted in FIG. 13. A divot marker 32 is very similar to an inwardlyextending force bump 20 in FIG. 11, but it is spherical rather thanelliptical and much smaller in diameter. To form a divot marker 32, thetechnician will identify a small round region of the point cloud atexactly the right position relative to the tooth under scrutiny. Thetechnician will select and push a master point near the center of theregion and all linked points will follow to a degree. The result is aseries of discrete, sharply formed concavities located here and there asrequired around the arch to serve as visual markers indicating theposition where holes will be installed relative to mal-positioned teeth.

Another point cloud-based operation is that of locating retaining tacks30, as described in FIG. 15, that serve to hold the entire aligner tray18 in place in the mouth. In summary, technician-located marker divotswould serve to mark locations for later installing pliers-formed holesfor the installation of the various types of aligner auxiliariesdescribed above. If the technician decides that an aligner tray 18 willbe cut into multiple sections, a series of divots can be used to markthe location of the cuts or sinuses.

Preparing the model to form aligners with windows or outset landsrequires methods that are different than those used to form bumps,bubbles and marker divots. Windows usually will have a plan-form oroutline following the edges of a portion of the crown of a tooth or theentire crown of a tooth. Such shapes are more Cartesian thanfootball-shaped bumps, bubbles and the round divot markers, andgenerally larger. Nonetheless, the CAD technician employing the methodsof the present invention can form a polygonal boundary around the regionof involved points of the point cloud, again creating a region thatincludes the linking of all of the points inside that boundary. Using adifferent point-linking algorithm however, the CAD technician can tug ona master point and all of the linked points of the point cloud withinthe designated region will follow equally. The point-linking logic willresult in the entire region standing outward from the tooth surface.Such a feature will later be present in the actual formed aligner andwill serve as a physical template or aid to the doctor or lab technicianin cutting away aligner material to form a window. Since it is a raisedplateau formed directly in the aligner, the doctor can easily see whatmaterial the technician had decided was necessary to remove.

As described above, elastic hooks and other aligner auxiliaries thatpop-in can be installed in an outset land in order to ensure that theirinwardly extending features do not contact teeth. In establishing outsetlands on the virtual model, the technician will use the samepoint-linking algorithms as used for establishing the shape and locationfor a window where all of the points come along with a tugged masterpoint equally.

As shown in FIG. 14, a round outset 34 has been formed by identifying acircular region of points and tugging all of those points outwardperpendicularly away from the tooth surface. As can be appreciated, whenan aligner is sucked down over such a pattern, a corresponding outsetland will be formed in the aligner. Once formed in the aligner, a holecan then be pierced at the center of the flat top of the outset using aspecial pliers, such as catalog item 82730, available fromRaintree-Essix, Metairie, La. Once a hole is pierced, any one of a groupof pop-in aligner auxiliaries can be installed as needed.

As previously described, tacks may be offered in a progression oflengths characterized as short, medium and long. In such a series, theincrease in length between a short tack and a medium tack and then to along tack may be about 0.75 mm. In a case where, for example, a toothneeds only a slight correction, or the exact amount of correction neededfalls in between the 0.75 mm increments between short, medium and long,a CAD technician may construct a discreet outset land of a preciselycontrolled height. For example, if a very short outset land were to beformed with a height of 0.37 mm, and a medium tack was installed in theoutset land, the forces applied to the underlying tooth would be equalto a tack falling approximately half way between a short and mediumtack. In this manner, devices of predetermined force-generatingdimensions may be further calibrated as needed by mounting them inoutset lands of selected heights.

Continuing with aspects of the present invention that lend themselves tovery precisely controlled corrective movements of teeth such as thosefinishing corrections needed to attain final aesthetic positioning atthe end of treatment, the following method is described through theexample of a lower incisor that is undesirably inclined lingually by 1mm. A CAD technician can form a virtual depression, similar to a divotor the depression associated with a bump 20, but sized and shaped toaccommodate the nose of a tack. Such a geometrically discrete depressionwill be formed on the lingual side of the virtual tooth near its incisaledge. The CAD technician will form the depression in the linguallyinclined lower incisor with a depth corresponding exactly to the amountof correction needed, in this case 1 mm deep. After the depression hasbeen formed, the CAD technician will bring a virtual model of a mediumtack into the virtual space and move it into close proximity with thedepression. Using a CAD step known as “mating”, the CAD technician willcause the nose of the tack to come into intimate contact with thedepression so that the tack 30 and the virtual model become one solidstructure, as shown in FIG. 15.

When a suck-down pattern is produced from this virtual model and analigner is then sucked down over it, the resulting aligner will exhibitan outset feature adjacent to the undesirably lingually-oriented toothcoinciding with the exposed portions of a tack projecting lingually outof the referenced mandibular incisor. When viewing the aligner(particularly that cavity from the inside), it will be seen that thelingual-outset feature extending lingually from the subject lowerincisor will have internal dimensions exactly corresponding to theexposed portions of the tack 30. The resilient nature of the alignermaterial permits the forcible placement of a tack into this outsetfeature. The tack will then be held and retained within the recess.

Most of the foregoing descriptions of various actions and operationsthat can be executed by a CAD technician in preparing aligners haveinvolved manipulations of the initial digital point cloud. Other typesof operations that a CAD technician may need to undertake can best beaccomplished after the point cloud has been further processed. Sincesuch operations involve the use of CAD software to construct precisefeatures on the virtual model, the first step in such a process is toconvert the point cloud data into a surface, and then into what is knownas a solid model. Software suitable for converting raw point cloud datainto complex biological surfaces are available for this purpose from thesources listed below: Raindrop Geomagic, Inc. P.O. Box 12219 ResearchTriangle Park, N.C. 27709 Lightwave Enterprises, Inc. 2396 InnovationWay Rochester, N.Y. 14624 Paraform, Inc. 3052 Bunker Hill Santa Clara,Calif. 95054. Once the point cloud has been converted to a surface, thesoftware is further used to close the surface. “Closing” here indicatesit should be understood that the teeth and a small portion of the gumsform a generally horseshoe shape. The surface defining the gums andteeth is in a mathematical sense infinitely thin. In CAD terminology, itis referred to as “lightweight”. If the lightweight horseshoe-shapeddental model is viewed from its rear surface, for example, it is seen asmerely a hollow shell. The software, in closing the surface, in effectputs a bottom on it. At this stage it may still be considered aninfinitely thin surface (i.e., lightweight), but with a bottom on it, ittakes on a quality known as “watertight”.

CAD software of the solid-modeling type such as is available fromSolidWorks Corporation, 300 Baker Avenue, Concord, Mass. 01742 and PTC(Pro-Engineer), 140 Kendrick Street, Needham, Mass. 02494, has thecapability of taking lightweight but watertight surfaces and convertingthem into standard, fully dense or fully solid models of the typenormally handled by solid modeling CAD software. Once converted to sucha solid, the resulting dental model can be manipulated in a CADenvironment in a conventional manner.

One of the operations that a CAD technician would then undertakeaccording to the methods of the current invention is the installation ofstructures emerging directly out of the virtual solid CAD model. Forexample, a structure may be constructed that is needed fordraft-retained inclusion devices. Two basic types of aligner auxiliarieswere described above. One group of aligner auxiliaries were described aspop-in and a second group was described as devices that must beinstalled in outset lands to prevent them from undesirably contactingteeth. A third group of aligner auxiliaries referred to as“draft-retained devices” can also be accommodated with the presentinvention. Modification of the CAD model for attachment ofdraft-retained devices is preferably done after the point cloud has beenconverted to a solid CAD-manipulatable model. CAD manipulations of asolid model are precise and generally more sophisticated than operationsinvolving the tugging or pushing on a point cloud.

As noted above, embodiments within the scope of the present applicationinclude program products comprising machine-readable media for carryingor having machine-executable instructions or data structures storedthereon. Such machine-readable media can be any available media that canbe accessed by a general purpose or special purpose computer or othermachine with a processor. By way of example, such machine-readable mediacan comprise RAM, ROM, EPROM, EEPROM, CD-ROM or other optical diskstorage, magnetic disk storage or other magnetic storage devices, or anyother medium which can be used to carry or store desired program code inthe form of machine-executable instructions or data structures and whichcan be accessed by a general purpose or special purpose computer orother machine with a processor. When information is transferred orprovided over a network or another communications connection (eitherhardwired, wireless, or a combination of hardwired or wireless) to amachine, the machine properly views the connection as a machine-readablemedium. Thus, any such connection is properly termed a machine-readablemedium. Combinations of the above are also included within the scope ofmachine-readable media. Machine-executable instructions comprise, forexample, instructions and data which cause a general purpose computer,special purpose computer, or special purpose processing machines toperform a certain function or group of functions.

It should be noted that although the figures herein may show a specificorder of method steps, it is understood that the order of these stepsmay differ from what is depicted. Also two or more steps may beperformed concurrently or with partial concurrence. Such variation willdepend on the software and hardware systems chosen and on designerchoice. It is understood that all such variations are within the scopeof the application. Likewise, software implementations could beaccomplished with standard programming techniques with rule based logicand other logic to accomplish the various connection steps, processingsteps, comparison steps and decision steps.

It will be appreciated therefore, that the present invention provides anew and useful method and apparatus for orthodontically aligning teeth.The method steps and the equipment, components, software and the likecan, of course, be changed or varied and still fall within the scope ofthe invention. The invention has been exemplified as described hereinand as shown on the drawings, and the actual scope of the inventionshall only be limited by the attached claims.

The invention claimed is:
 1. A method of fabricating an orthodonticaligner tray comprising: segmenting teeth represented by an originaldigital model of a patient's teeth; repositioning at least one of theteeth represented by the original digital model from an originalposition to a final position to create a final digital model of thepatient's teeth, the final digital model representing a final teethposition to be achieved by an orthodontic treatment plan; superimposingthe final digital model onto the original digital model to create anoverlay model; fabricating a plurality of identical aligner trays basedon the overlay model, each tray having a tooth-receiving compartmentsuch that the original position, final position, and a movement pathwayfrom the original position to the final position are within thetooth-receiving compartment of the aligner and forming the plurality ofidentical aligner trays as passive aligner trays; identifying a positionfor a first force appliance in a first aligner tray; identifying aposition for a second force appliance in a second aligner tray; andinserting the first and second force appliances into their correspondingaligner trays, the first and second force appliances positioned withinthe tooth-receiving compartment of its corresponding aligner tray toexert a selected force upon a tooth to be repositioned.
 2. The method ofclaim 1, wherein the step of fabricating comprises creating a rapidprototype model of the overlay model.
 3. The method of claim 2, whereincreating the rapid prototype model is performed by one ofstereolithography, laser sintering or fused deposition.
 4. The method ofclaim 1, wherein the original digital model of a patient's teeth isobtained by pouring a stone model from a patient's dental impression andscanning the stone model into a digital file.
 5. The method of claim 1,wherein the original digital model of a patient's teeth is obtained byperforming an intraoral scan of the patient's dentition.
 6. The methodof claim 1, further comprising analyzing a case using an inter-proximalreduction (IPR) prescription and desired tooth movements.
 7. The methodof claim 6, wherein the step of analyzing comprises reviewing the IPRprescription for validity; performing IPR if the IPR prescription isacceptable; and developing the orthodontic treatment plan.
 8. The methodof claim 1, wherein the step of fabricating the aligner trays furthercomprises vacuum thermoforming the aligner trays over a physicalrepresentation of the overlay model using a vacuum forming machine and aplastic thermoforming sheet.
 9. The method of claim 1, wherein the stepof identifying a position for the first force appliance in the firstaligner tray comprises digitally establishing a divot marker on adigital model of the patient's teeth intermediate the original digitalmodel and the final digital model.
 10. The method of claim 9, whereinthe step of digitally establishing the divot marker comprisesidentifying and selecting a master point near a center of a desiredregion on the digital model of the patient's teeth at a pointintermediate the original position and the final position within theoverlay model.